1. Field of the Invention
The present invention relates to a method of detinning a Sn layer and/or a CuSn layer of a Sn plating layer formed on a Cu-based material to recycle the Cu-based material.
2. Description of the Related Art
A Cu-based material including a copper-based alloy containing one or more of elements of Fe, Ni, Si, Sn, P, Mg, Zr, Cr, Ti, Al, Ag and so on in a range of several hundreds mass ppm to 30 mass %, in addition to pure copper, brass, or phosphor bronze is made from an ingot via processes of rolling, annealing and so on and finished as a bar rod or a wire rod with a plate thickness of 0.1 to 4.0 mm, and then widely used for current-carrying parts such as terminal, bus bar, spring and the like for vehicle, for household appliance or for industrial instrument. Such a Cu-based material is generally used after it is plated with Sn that is relatively inexpensive among plating metals at a thickness of 0.5 to 5.0 μm in order to secure contact reliability at application of current and corrosion resistance. Due to reflow treatment or aging of the Sn plating, a CuSn diffusion layer mainly composed of intermetallic compound such as Cu6Sn5, Cu3Sn or the like is formed between the Cu-based material and the Sn plating or between a Cu base plating and the Sn plating when the Cu base plating has been applied between the Cu-based material and the Sn plating, and the thickness of the CuSn diffusion layer is about 0.2 to 2.0 μm. Further, the layer of Sn which has not been consumed for the formation of the CuSn diffusion layer but remains on the uppermost surface side of the Sn plating is called a Sn layer.
Until the Cu-based material such as a plate material or the like to which Sn plating has been applied is formed into a product of a current-carrying part, slitting process, pressing process or the like is generally performed after the Sn plating, and scraps are generated during the processing. If the scraps are molten as they are as a raw material, the molten material contains much Sn component corresponding to the plated Sn and cannot be reused as a raw material of the Cu-based material that is the original material. Therefore, to reuse the original material, detinning the plated Sn is conceivable.
Conventionally proposed methods as a method of detinning the Sn plating on the Cu-based material are electrolysis in sodium hydroxide and immersion into sulfuric acid or nitric acid containing Cu ions as disclosed in Japanese Laid-open Patent Publication No. S58-87275.
Further, Japanese Laid-open Patent Publication No. 2000-226214 discloses, as a method of dissolving Sn in a method of producing a high-purity alkali stannate compound, a method of dissolving Sn while dripping a hydrogen peroxide solution as a reaction accelerator into an alkali hydroxide solution.